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Questa Rock Pile Weathering and Stability Project GEOLOGIC SETTING AND MINING HISTORY OF THE QUESTA MINE, TAOS COUNTY, NEW MEXICO Virginia T. McLemore May 18, 2009 New Mexico Bureau of Geology and Mineral Resources Open-file Report OF-515 Molycorp Task 1.2.2, B1.1 1 TABLE OF CONTENTS INTRODUCTION AND PURPOSE .................................................................................. 4 CLIMATE........................................................................................................................... 5 GEOLOGIC AND TECTONIC HISTORY ....................................................................... 7 Structural Setting ........................................................................................................... 12 San Luis basin................................................................................................................ 12 Red River....................................................................................................................... 13 Glaciation....................................................................................................................... 13 MINING HISTORY ......................................................................................................... 14 Questa district................................................................................................................ 14 Red River-Rio Hondo district........................................................................................ 15 Twining District............................................................................................................. 17 MINERALIZATION AND ALTERATION AT QUESTA............................................. 17 Formation of Questa Molybdenum Deposit .................................................................. 17 Alteration associated with the Questa deposit............................................................... 19 ALTERATION SCARS ................................................................................................... 20 SUMMARY...................................................................................................................... 22 ACKNOWLEDGEMENTS.............................................................................................. 22 REFERENCES ................................................................................................................. 23 FIGURES FIGURE 1. Location of the Questa and other mining districts in Taos County (McLemore and Mullen, 2004)................................................................................................... 4 FIGURE 2. Location of the Questa mine within the Red River basin. Heavy green line delineates the upper Red River watershed.............................................................. 5 FIGURE 3a. Simplified geologic map of the southern portion of the Questa Caldera in the vicinity of Red River, New Mexico from Ludington et al. (2005) modified from Lipman and Reed (1989). The individual rock types shown are a starting point for conceptualizing what might be significant units or domains in the study area. Lithologies are described in more detail in the lithologic atlas (McLemore et al., 2009). Note that the areas impacted by hydrothermal alteration (alteration scars) are outlined in orange. Key in Figure 3b and cross section A-A’ in Figure 3c............................................................................................................................. 8 FIGURE 3b. Key to geologic map in Figure 3a, from Ludington et al. (2005) modified from Lipman and Reed (1989)................................................................................ 9 FIGURE 3c. Cross section along line A-A’ in Figure 3a, from Ludington et al. (2005) modified from Lipman and Reed (1989) .............................................................. 10 FIGURE 4. Tectonic geologic setting of the Questa-Red River area (modified from Meyer and Leonardson, 1990; Meyer and Foland, 1991)..................................... 12 FIGURE 5. Cirques and moraines on the northeastern slopes of the mountains south of the Questa mine..................................................................................................... 14 FIGURE 6. Topographic map of the Red River valley showing alteration scars (yellow), debris fans (light blue), ore bodies (red), and the Questa mine (black) (from Ludington et al., 2005).......................................................................................... 16 2 FIGURE 7. Cross section showing schematic spatial distributions of lithologies, alteration assemblages, and alteration scars in the Red River valley (taken from Ludington et al., 2005, which is modified from Martineau et al., 1977).............. 18 FIGURE 8. Schematic sketch of forms of porphyry molybdenum deposits that are dependent upon the amount of fluid in the source magma, overpressures, host rock permeability, and other physical/chemical characteristics (modified in part from Ross et al., 2002; Guilbert and Park, 1986) ................................................. 19 FIGURE 9. Map showing the alteration scars and mineral deposits of the Red River area. Alteration scar names from Meyer and Leonardson (1990) ................................. 20 TABLES TABLE 1. Monthly climatic summaries from 1/1/1915 to 4/30/2007 for Red River, NM (from Western Regional Climate Center, 2007). min=minimum, max=maximum, temp=temperature, prec=precipitation.................................................................... 6 TABLE 2. Summary climate statistics for the primary weather stations at the Questa mine (more details in Golder Associates Inc., 2005)....................................................... 6 TABLE 3. Summary of geologic history of the Questa area (Bauer et al., 2004; Ludington et al., 2005; Samuels, 2008; Zimmerer, 2008)...................................... 7 3 INTRODUCTION AND PURPOSE The Chevron Mining Inc. (formerly Molycorp, Inc.) Questa molybdenum mine is located on the western slope of the Taos Range of the Sangre de Cristo Mountains of the Southern Rocky Mountains near the edge of the Rio Grande rift in north-central New Mexico (Fig. 1). It is on N.M. Highway 38, between Questa and Red River. The mine is on southward facing slopes and is bounded on the south by Red River (elevation of approximately 7500 ft) and on the north by the mountain divides (elevation approximately 10,750 ft) (Fig. 2). The geology and mining history of the area is complex and is summarized in this report from Carpenter (1968), Clark (1968), Reed et al. (1983), Lipman (1988), Meyer and Leonardson (1990), Czamanske et al. (1990), Roberts et al. (1990), Ludington et al. (2005) and others as cited. Lithologies likewise are diverse, ranging from metamorphic rocks to volcanic rocks to granites to shales, limestones, and sandstones. The purpose of this report is to summarize the geologic setting and mining history in the Questa-Red River area in order to provide a framework for the Questa Rock Pile Weathering and Stability Project (QRPWASP) with emphasis on interpretations from recent references. Descriptions of the various lithologies, including photographs, mineralogy, and chemical analyses are presented in a separate lithologic atlas (McLemore et al., 2009). FIGURE 1. Location of the Questa and other mining districts in Taos County (McLemore and Mullen, 2004). 4 FIGURE 2. Location of the Questa mine within the Red River basin. Heavy green line delineates the upper Red River watershed. Vegetation within the area includes Douglas Fir, Engelman spruce, Ponderosa pine, Gambel oak, mountain brome, kinnikkinnik, aspen, Kentucky bluegrass, Arizona fescue, and whortleberry (Hagan, 2001). Along the valley floor, the alpine to sub-alpine community gives way to a meadow or riparian corridor including willow, narrowleaf cottonwood, various grasses, and shrubs, including wild rose, Rocky Mountain clematis, scotch broom, and squawberry. The steeper, rockier north slope of the canyon favors fir and spruce, while the south slope of the canyon shows more aspen, narrowleaf cottonwood, and other undergrowth. CLIMATE The climate at the Questa mine is semi-arid, with cold snowy winters and moderate warm summers with monsoons during July and August. Summer rains often cause mudslides and flash floods that have blocked the highway at times. The Red River drainage receives an average of 20.6 inches of precipitation per year, concentrated mostly in July and August (Table 1; Hagan, 2001; Western Regional Climate Center, 2007). The record maximum winter snowfall for New Mexico is 483.0 inches in 1911-12 at the Anchor mine near Red River and the record maximum 1-day snowfall for New Mexico is 36.0 inches on March 12, 1978 at Red River (Western Regional Climate Center, 2007). The record maximum annual precipitation in New Mexico is 62.45 inches in 1941 at White Tail (near Cloudcroft) and the record maximum 24-hour precipitation is 11.28 inches on May 18-19, 1955 at Lake Maloya (near Ruidoso; Western Regional Climate Center, 2007). The average annual pan evaporation rate for Eagle Nest (southwest of Red River) is 42.96 inches as measured from 1937 to 2005, with most of the evaporation occurring from April through October (Western Regional Climate Center, 2007). Eagle Nest, Cloudcroft, and Lake Maloya are in mountainous areas similar to the Questa mine. The differences in relief between the Questa rock piles result in large variations in temperature and precipitation

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